1. Field of the Invention
The invention is directed to blends of aromatic carbonate polymers with particular ABS compositions of very high rubber content made by emulsion polymerization, in particular to such blends with low gloss, good retention of physical properties and in particular retention of properties on heat aging.
2. Brief Description of the Prior Art
It has long been known that ABS thermoplastics can be blended with aromatic carbonate polymers, such as polycarbonates, to make useful thermoplastic blends with enhanced impact strength. A brief survey of such blends was given by Chiang et al. in Polymer Engineering and Science, 27 (9), 632-639 (May 1987) and by Suarez et al. J. Appl. Polymer Sci., 29, 3253 (1984). Chiang et al. describe the use of ABS having 32% rubber content.
However, to achieve commercially useful combinations of properties has required extensive experimentation and many such combinations are not useful, and the special advantages of particular ABS types have not been fully recognized. As shown by Chiang et al. (loc. cit.) the properties of polycarbonate-ABS blends are not obvious averages of the properties of the components. It has been especially difficult to achieve polycarbonate-ABS blends with good heat aging properties. It has also been difficult to achieve such blends with good weld line strength such that molded objects made using molds with multiple points of entry are free of weakness at the region where the molten polymer streams join in the mold. Another major shortcoming of polycarbonate-ABS blends has been that it has been difficult to achieve low-gloss properties without loss of physical properties. This is not surprising because the low-gloss property arises from formation of domains or phases of optical dimensions, and the requirements for the separation of the components to form such phases tends to work against optimal strength properties and in the extreme can even aggravate delamination and provoke weak weld lines in molded articles.
A matte or non-glossy surface is often preferable for products such as housings for computer terminals, typewriters, miscellaneous electrical appliances and automotive parts, but these uses are equally demanding of good thermomechanical properties, good heat aging and strong weld lines.
The present invention provides low-glass aromatic carbonate polymer-ABS blends with good impact strength, good heat aging properties, and strong weld lines. The simultaneous achievement of all these desirable properties is accomplished by the use of certain specific types of ABS at a certain percentage by weight, whereas in general by use of other types of ABS, or other percentages, these properties will not be achieved all at the same time.